Shopping apps let you buy fast on your phone and offer discounts and rewards when you shop in-store. But for some retail apps, that convenience has a price: privacy. The way retailers online track your shopping habits with cookies, some brick-and-mortar retailers are using apps that access your phone’s GPS to track your location in the real world. The tip-off may be the timing of notifications that pop up when you are in close proximity to a store. We asked shoppers in Philadelphia if they had any unusually well timed app notifications. One woman said that when she came to a certain location on 69th Street on her walk to work, an ad for the Gap popped up offering her a coupon to go shopping. Another shopper said the Urban Outfitters app seemed to know where he was, “Whenever I come within like 50 feet I get like, ‘hey did you know there’s a sale ending in a couple days?'” And others wondered why apps from Target and Macy’s asked to access their location when they were installed. According to University of Pennsylvania professor Joseph Turow, many shopping apps now use a phone’s GPS to access your location. They have technologies that can follow you as you walk through sectors of the store and can connect to your data, so they know who you are,” he said. Read more at ABC News.